High pressure reinforced hydraulic hose is typically used on a variety of fluid power operated machines, such as earth-moving machines, to provide a flexible connection between several moving parts of a hydraulic circuit employed on or within the machine. Such hoses may include a hollow polymeric inner tube on which successive cylindrical layers of reinforcing material, such as wire or textile, are concentrically applied to contain the radial and axial pressures developed within the inner tube.
Many applications are demanding hose constructions with both high burst strength and long term fatigue resistance. Using conventional technology, the burst strength of a hose design may be increased by adding additional reinforcing material and/or layers, a practice which is generally discouraged because of its negative impact on the flexibility of the hose, or by universally increasing the tensile strength of each layer of reinforcement material, which may come at the expense of hose fatigue resistance.
To determine the robustness of a hose design, a hose manufacturer typically performs, among other tests, an impulse test and a burst test on the hose. An impulse test measures a hose design's resistance to fatigue failure by cyclically subjecting the hose to hydraulic pressure. A burst test, on the other hand, is a destructive hydraulic test employed to determine the ultimate strength of a hose by uniformly increasing internal pressure until failure. Based on these and other tests, a manufacturer can estimate a hose life that can be used to determine when a hose has reached the end of its life and may require replacing.
In some circumstances, it is desirable to detect, in a non-destructive and non-disruptive manner a likelihood of failure of a hydraulic hose. One solution providing this capability is discussed in U.S. Pat. No. 7,555,936, and discloses connecting a monitor circuit between two parallel, at least partially-conductive layers of a hose wall. A change in an electrical property observed by that monitor circuit may indicate a change in a property of the hose wall structure that might indicate impending failure of the hose wall.
However, even with this solution, it can be difficult to determine whether the changed electrical property is in fact due to a change in a physical feature of a hose wall, or if the changed electrical property is due to a change in the sensing electronics, a change in an electrical property of a harness connecting the monitoring circuit to the hose wall, or simply degradation of an electrical connection to the hose wall. In these cases, there may be a change in an electrical property observed, even when hose wall integrity is not compromised.
For example, during normal use of such a hose, the hose and associated electrical connections thereto may become dirty or corroded by various environmental and use-case means. This corrosion effect should be monitored (and possibly compensated for) in order to ensure the best connection to and reading of the electrical characteristics of the hose.
Monitoring for electrical changes in a hose assembly can be difficult. This is because such electrical changes are likely to be, fleeting, at least during early failure events. For example, a pressure pulse occurring in a hydraulic hose can cause a momentary change of an electrical characteristic at the time of the pulse, but which reverts to a normal electrical characteristic after the pressure pulse event. If a monitoring circuit operates non-continuously, in that it does not provide constant monitoring of the electrical characteristic, it may be possible that the change in electrical characteristic occurring during the pulse is not detected.
For these and other reasons, improvements are desirable.